These Deep Sea Vents Hint At The Origins Of Life

At the origin of life, the first protocells must have needed a
vast amount of energy to drive their metabolism and replication,
as enzymes that catalyze very specific reactions were yet to
evolve.

So where did all that energy come from on the early Earth, and
how did it get focused into driving the organic chemistry
required for life?

Nick Lane at the University College London and Bill Martin at the
University of Dusseldorf address those questions—and why all life
as we know it conserves energy in the peculiar form of ion
gradients across membranes—in their research published in the
journal Cell.

“Life is, in effect, a side-reaction of an energy-harnessing
reaction. Living organisms require vast amounts of energy to go
on living,” says Lane. “It is possible to trace a coherent
pathway leading from no more than rocks, water, and carbon
dioxide to the strange bioenergetic properties of all cells
living today.”

Humans consume more than a kilogram (more than 700 liters) of
oxygen every day, exhaling it as carbon dioxide. The simplest
cells, growing from the reaction of hydrogen with carbon dioxide,
produce about 40 times by mass as much waste product from their
respiration as organic carbon.

In all these cases, the energy derived from respiration is stored
in the form of ion gradients over membranes.

This strange trait is as universal to life as the genetic code
itself.

Lane and Martin show that bacteria capable of growing on no more
than hydrogen and carbon dioxide are remarkably similar in the
details of their carbon and energy metabolism to the
far-from-equilibrium chemistry occurring in a particular type of
deep-sea hydrothermal vent, known as alkaline hydrothermal vents.

Based on measured values, they calculate that natural proton
gradients, acting across thin semi-conducting iron-sulphur
mineral walls, could have driven the assimilation of organic
carbon, giving rise to protocells within the microporous
labyrinth of these vents.

They go on to demonstrate that such protocells are limited by
their own permeability, which ultimately forced them to transduce
natural proton gradients into biochemical sodium gradients, at no
net energetic cost, using a simple Na+/H+ transporter.

Their hypothesis predicts a core set of proteins required for
early energy conservation, and explains the puzzling promiscuity
of respiratory proteins for both protons and sodium ions.

These considerations could also explain the deep divergence
between bacteria and archaea, single celled microorganisms.